Street-light CCT debate will continue,but it is misguided

We have written about the debate
over LED street-light color temperature or CCT. I remain convinced
that cooler CCTs, perhaps in the
4000K range, are optimum because
I believe we see better at night
under such conditions. Of course,
the American Medical Association
(AMA) and others have voiced
opposing opinions ( http://bit.ly/2e W91WB).

The solid-state lighting (SSL) industry has
certainly reacted to public outcry, although I
believe that outcry is from a vocal minority.
Lighting manufacturers are delivering more
products at warmer CCTs. For example, Cree
launched its light-guide-based RSW luminaire at 3000K and recently added a 2700K
version ( http://bit.ly/2q TkJ Y0). But the fact is
CCT doesn’t matter in any case, while spectral power distribution (SPD) is critical. And
the US Department of Energy (DOE) has new
research that suggests LED street lights are
not impacting sky glow to the extent warm-CCT advocates have claimed. We also have
a compelling feature that explains how you
can have a cool CCT with none of the feared
blue energy in the SPD.

Let’s start with the DOE work. The agencyset out to study typical LED street lightsbeing broadly deployed and compare themwith legacy HID street lights using sourcessuch as high-pressure sodium lamps.

The research is based on around 200,000
computer simulations of commercially-available LED and HID street lights with
sets of modeling runs changing one variable at a time. The LED street lights generally are more directional than HID street
lights, so in many cases, the LED installations will contribute less light spill to sky
glow. Indeed, the DOE said some of the LED
luminaires generate as little as 20% of the
uplight of legacy products in unweighted
tests. In fairness, some of the LED products also generate more uplight.

Still, the results are encouraging. The
research assumes ground reflectivity of
15%; essentially, that is the only source
of uplight with well-designed LED luminaires. The DOE said that for a far observer
located 40 km from a city center, LED and
beam-forming optic technologies reduce the
contribution of street lights to sky glow by
95%. You can find more details in our news
( http://bit.ly/2qU0QAV).

The DOE emphasized a point I have maderepeatedly. The problem is operationallight levels. Street lights can and should bedimmed. And poor lighting design contrib-utes more to sky glow than LED technologyat cool CCTs. The DOE emphasized that CCTis not an appropriate way to characterizestreet lights for either sky glow or as a blue-light hazard for human eyes.

We also have a feature article from Soraa
that supports the point about CCT and SPD
(p. 45). Soraa has used a violet emitter in
phosphor-converted white LEDs, whereas
most of the industry uses a blue pump.
The violet pump has been part of a strategy to render whites and colors optimally
( http://bit.ly/VFt9D2).

But with public concern over a blue hazard, Soraa is using the violet-based technology to address any fears. The company is
developing LEDs that have a complete lack of
energy in the blue region that is known to be
a hazard. Yet phosphor technology and the
violet pump will allow the company to produce any CCT with high CRI performance.

It remains to be seen how the Soraa technology will come to market. The company
has not sold its LEDs at the component level
in the past. We should learn more soon.

Meanwhile, I’d hope that the naysayers
learn more about what really matters.